1. Field of the Invention
This invention relates to compact optical systems, especially to portable optical systems adapted to project images across the wearer's field of view. The invention has particular, but not exclusive, application to the provision of head-up display images for aircrew, and provides a means by which an optical system may be employed to convert an image provided by a small cathode ray tube (CRT), matrix array or other light source (typically mounted on the flying helmet) into a collimated, head-up form suitable for the display of information. Other possible applications of the invention are in connection with military and high-performance vehicles.
2. Discussion of Prior Art
There is an increasing need for this provision in both fixed and rotary-wing aircraft, the information to be displayed being required to complement the electronic display facilities installed in the aircraft cockpit. Whilst any presentation of information in a head-up format (in accordance with established criteria) will enhance operator performance, a particularly useful facility provided by head-mounted displays would be the display of information superimposed over the viewer's outside view in whatever direction the viewer's head was pointing.
Unfortunately, severe inertia and volume constraints are placed on the provision of equipment supported on the human neck, and in this respect particularly strict limits are imposed for fast-jet applications where a need for greater head freedom compounds difficulties already aggravated by the effects of high-g manoeuvres. Other requirements, essential for fast-jet operation, such as the provision of safe ejection and birdstrike protection, are not needed in rotary wing operations which are restricted to a much smaller flight envelope with no requirement for emergency ejection (in the same sense). For the latter applications it is therefore relatively straightforward to supply more facilities and to achieve a higher technical performance.
Nevertheless for all these applications there is a demand for maximum performance for the minimum size and weight, and this invention is intended to provide apparatus which is physically acceptable and can provide a good optical performance and range of facilities.
Certain proposals have been made for projecting a head-up display from helmet-mounted components, such as those described in EP-A-11,024, and for the design of individual components, such as eye position sensors as described in EP-A-408,344, but hitherto no proposal has been made for a system which effectively integrates the optical components in a way which meets the requirements set out above.